The present invention relates to a process for the preparation of polyolefin/inorganic component nanometer-composite(the xe2x80x9cnanomneter-compositexe2x80x9d herein is abbreviated to xe2x80x9cnanocompositexe2x80x9d thereinafter) by in-situ polymerization, more particularly, to a process for the preparation of a tertiary component nanocomposite consisting of silica (or titanium dioxide), layered metal compound and polyolefin.
It is well known that the properties of conventional polymers can be improved by addition of certain inorganic components. In general, the inorganic components in the polymeric material are difficult to be homogeneously dispersed and will separate out after a relatively long time, thus both largely deteriorating the comprehensive properties of the material.
If the dispersion of the inorganic component in the polymeric materials approaches nanometric scale, mechanical propertics, thermal stability, gas permeability, optical properties, self-extinguishing characteristics and the like of the nanocomposite will be greatly improved without degrading the properties of the pure polymeric material even when the proportion of the inorganic component is very low, for example, less than 5% by weight.
Examples of inorganic component of nanometer size in an organic/inorganic nanocomposite include nanometer ball-shape in all three dimensions such as nanometer granules, or nanometer size in two dimensions such as whiskers, and nanometer size sheet structure such as layered metal compounds. Polymeric materials using layered metal compounds as the nanometer component can be obtained by the following three methods:
1) exfoliation adsorption methodxe2x80x94An aqueous solution of water soluble polymer molecules interacts with inorganic layers of nanometer size in complete exfoliated form to form a composite;
2) melt intercalationxe2x80x94Polymer in molten state is intercalated under external stress into interlayer gaps of the modified layered metal compound to form a nanocomposite;
3) in-situ polymerizationxe2x80x94Monomer or catalyst is adsorbed in the gaps of the layered metal compound and then is polymerized in the gaps, as a result, the inorganic component is homogeneously dispersed in the polymer matrix.
The object of the present invention is to provide a process for the preparation of a polyolefin/inorganic component nanocomposite by in-situ polymerization. According to the present method, silica or titanium dioxide particles are assembled in the gaps of the layered metal compound by sol-gel method; sequentially, metallocene catalyst is loaded, and then olefine(s) is(are) in-situ polymerized. Nanocomposites filled with layered metal compound and spherical or sphere-like nanometer inorganic component are finally obtained. The distance between the layers is thus increased due to the incorporation of silica or titanium dioxide nanometer particles into the gaps between layers of the layered metal compound, so it is easier for metallocene catalyst to enter the gaps of the layered metal compound. At the same time, abundant hydroxyl groups on the intercalated silica or titanium dioxide particles could further raise the amount of the metallocene catalyst loaded. Since the said layered metal compound possesses larger interlayer distance and suitable passages, ethylene monomer could diffuse freely into the gaps to contact with the metal ions on the catalyst centers. Large amount of heat generated in the polymerization helps the silica or titanium dioxide particles to disperse homogeneously at nanometer level in the polyolefin matrix.
According to the present invention, layered metal compound is firstly mixed with water to form an aqueous suspension of 0.5%-10% by weight, and the resulting suspension is then mixed with an aqueous solution of a long-chain alkyl ammonium salt in an amount of 1-2 times of exchange value of the layered metal compound by weight to form a layered organo-metal compound, and the resulting compound is then dried in air at room temperature for 10-40 h, where, the layered metal compound is montmorillonite or vermiculite, and the long-chain aliphatic ammonium salt is hexadecyl trimethyl ammonium bromide or decyl trimethyl ammonium bromide, and the water used is deionized water by ion exchange. To the dried organo-metal compound is added aliphatic amine and the resulting mixture is stirred at 10-50xc2x0 C. for 20-60 min, wherein the mole ratio of layered organo-metal compound and aliphatic amine is in the range of 1:2-20, and the aliphatic amine used is C6H13NH2, C8H12NH2, C10H21NH2 or C12H25NH2. Then silica or titanium dioxide precursor is added into the aliphatic amine-treated layered organo-metal compound and the resulting mixture is stirred at 10-50xc2x0 C. for 3-6 h; the mole ratio of the precursor and aliphatic amine is 8-10:1. The precipitate is collected, dried at room temperature for 12-24 h and then dried at 100-300xc2x0 C. 10-30 ml/g of alkyl aluminum or alkoxy aluminum is added under inert gas atmosphere into the dried product and treated at 20-80xc2x0 C. for 12-24 h, the treated product is then washed with inert hydrocarbon solvent to remove the excess alkyl aluminum or alkoxy aluminum, silica or titaniumn dioxide precursor is tetraethyl orthosilicate, tetramethyl orthosilicate, tetraethyl orthotitanate, tetrabutyl orthotitanate, or methyl triethoxy silane, the inert organic solvent is toluene, hexane, heptane or petroleum ether. To the treated product, toluene solution of metallocene catalyst (19.38 mmole) is added at 20-80xc2x0 C., the added quantity being 10-40 ml for each gram of the carrier. The unloaded metallocene catalyst is removed by washing with toluene. The loaded catalyst is put into polymerization vessel followed by introducing ethylene or propylene monomer, wherein alkyl aluminoxane is used as the co-catalyst to carry out the olefin polymerization. HCl solution of ethanol is used to terminate the reaction.
Polyolefin nanocomposite filled jointly by layered metal compound and nanometer level silica or titanium dioxide can be prepared by the method according to the present invention. Due to the synergistic enhancement effect of the two kinds of nanometer particles, the mechanical properties of the polyolefin materials thus obtained will be greatly increased even if the content of the inorganic component is extremely low. In addition, the method for preparation of the catalyst is simple and the mechanical properties of the nanocomposite is high. Young""s modulus of the nanocomposite is in the range of 700-2600 MPa, while the tensile strength is in the range of 20-55 MPa.